The overall objective of the proposed project is to design an apparatus procedure to extend the vitality of stored human platelet concentrates for transfusion. TRA proposes to conduct experiments that will simulate condition of microgravity storage and at the same time keep most of the platelets away from the bag walls using ultrasound. Other experiments will investigate the effect of platelet/wall interactions in the absence of ultrasonic levitation. The results will allow comparison of these techniques with those obtained on NASA's space mission and with the existing data using standard storage techniques. This proposal, therefore, addresses itself to the question of the effect of the bag wall on the shelf-life of the stored platelets. If the storage bag wall is found to play a significant role in platelet activation, Phase II will develop a system for prolonging the viability of platelets during storage.